In magnetic bearings or suspensins for rotors or shafts, the rotor is generally maintained in a contactless state relative to the stator by magnetic field forces which are kept in balance.
For example, in German patent document (Open Application-Offenlegungsschrift) DE-OS No. 14 72 413, a magnetic suspension arrangement for an upright shaft is disclosed in which two annular permanent magnets are provided for the radial stabilization of the rotor on the latter and confront two annular permanent magnets of the stator with opposite polarity. The axial stabilization is provided by a disk formed on the end of the shaft of ferromagnetic material and a cup-shaped magnet on the stator juxtaposed with this disk. The latter magnet is energized electrically under the control of field plates which are disposed between the disk and the cup-shaped magnet and which operate through a circuit for controlling coil energization for maintaining the axial position substantially constant.
This system has the disadvantage that the cup-shaped magnet and the associated disk take up space which could be more usefully exploited otherwise and make the entire assembly bulky and difficult to incorporate into an apparatus in which the magnetic suspension would otherwise be advantageous.
Reference may also be made to the following patent documents which are relevant to magnetic suspension bearings and assemblies: German patent No. DE-OS No. 23 41 766 and U.S. Pat. Nos. 3,243,238, 3,888,553 and 3,512,851.
For an explanation of the operation of magnetic field plates as magnetic field plates, as magnetic field sensors, and the associated circuitry, reference may be had to Siemens Data Book 1976/1977 Galvanomagnetic Devices, Siemens AG, Munich Germany, p. 51 ff., in which the field plates are referred to as magneto resistors.
It is also known to provide a magnetic suspension which has at each end of the shaft two annular ferromagnetic bodies which are spaced apart.
In the region of the ferromagnetic bodies, the stator is provided with two annular permanent magnets between which an annular controllable electromagnetic element is provided with a ferromagnetic core. While the electromagnetic element combination with the ferromagnetic body of the rotor and the permanent magnets effects a radial stabilization, this system cannot be effectively used for axial stabilization except through detecting the axial rotor position and controlling the magnetic field of a further annular electromagnet which varies and stabilizes the magnetic forces acting in the axial direction. This suspension is capable of balancing forces but not moments and for complete suspension or journaling, still a second suspension element is required.
The other magnetic suspensions of the aforementioned patent documents, while being capable of maitaining a rotor in suspension, have various disadvantages including large size, complex construction and inability to be provided in an extremely reliable and compact configuration.